Secondary bending stress at nozzles (pressure vessel design manual)

[Klikoos]

I am sure many of you are familiar with the Pressure Vessel Design Manual by Dennis Moss.

In the design manual there is mention of a secondary bending stress along the hard axis on the nozzle. However, could somebody elaborate how a bending stress arises and in what direction this stress is?


For reference, here is the formula I am trying to understand;

 

[MrPDes]

What is a hard axis?

The internal pressure causes an outwards thrust force on the nozzle, therefore there will be bending stresses in the shell (and neck) local to the junction. The stresses will be similar to those calculated by WRC 107 with an outward thrust load.